Stability of Crystal Nuclei of Poly (butylene isophthalate) Formed Near the Glass Transition Temperature.

Silvia Quattrosoldi,Christoph Schick,Nadia Lotti,Michelina Soccio,René Androsch

doi:10.3390/polym12051099

Silvia Quattrosoldi, Christoph Schick + Show 3 more

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https://doi.org/10.3390/polym12051099

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Abstract

Tammann’s two-stage crystal-nuclei-development method is applied for analysis of the thermal stability of homogenously formed crystal nuclei of poly(butylene isophthalate) (PBI) as well as their possible reorganization on transferring them to the growth temperature, using fast scanning chip calorimetry. Crystal nuclei were formed at 50 °C, that is, at a temperature only slightly higher than the glass transition temperature, and developed to crystals within a pre-defined time at the growth temperature of 85 °C. The number of nuclei, overcritical at the growth temperature, was detected as a function of the transfer-conditions (maximum temperature, heating rate) by evaluation of the developed crystal fraction. For different size-distributions of crystal nuclei, as controlled by the nucleation time, there is detected distinct reduction of the nuclei number on heating to maximum temperatures higher than about 90 to 110 °C, with the latter value holding for longer nucleation time. Longer nucleation allows for both increasing the absolute nuclei number and generation of an increased fraction of larger nuclei. Heating at 1000 K/s to 140–150 °C causes “melting” of even the most stable nuclei. While direct transfer of crystal nuclei from the nucleation temperature (50 °C) to the growth temperature (85 °C) reveals negligible effect of the transfer-heating rate, in-between heating to higher temperatures is connected with distinct nuclei-reorganization above 85 °C on heating slower than 1000–10.000 K/s. The performed study not only provides specific valuable information about the thermal characteristics of crystal nuclei of PBI but also highlights the importance of proper design of Tammann’s nuclei development experiment for analysis of nuclei numbers. With the evaluation of critical rates of temperature-change for suppression of non-isothermal formation of both nuclei and crystals, the kinetics of crystallization of the slow crystallizing PBI is further quantified.

Highlights

Poly(butylene isophthalate) (PBI) is a linear aromatic polyester with a chemical structure similar to the well-known isomer poly(butylene terephthalate) (PBT) [1]
In case of PBT, the ester groups are in para-position, while in PBI they are in meta-position to each other
The PBI was synthesized as described in detail elsewhere [27]

Summary

Introduction

Poly(butylene isophthalate) (PBI) is a linear aromatic polyester with a chemical structure similar to the well-known isomer poly(butylene terephthalate) (PBT) [1]. Melt-crystallization of PBI is fastest between around 80 and 100 ◦ C, with the minimum crystallization halftime being of the order of magnitude of several minutes [17,18] Such a slow crystallization is a major drawback when attempting to obtain a semicrystalline structure for specific engineering uses through industrial processing routes, and it seemingly limits its commercial application. This notwithstanding, excellent mechanical behavior, good barrier properties, and easy melt-processability are reported for PBI [19], with ongoing research including its derivatives, such as end-capped materials, block copolymers, and random copolymers [19,20,21,22,23,24,25,26], for possible application, e.g., as hot-melt adhesive or coating

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